A comparative study of calorimetric methods to determine the crosslinking degree of the ethylene-Co-vinyl acetate polymer used as a photovoltaic encapsulant

Abstract

EVA copolymer foils are widely used as encapsulants for photovoltaic (PV) cells in PV modules. These foils need to be crosslinked during module manufacturing, to enhance their properties. Accurate and reliable methods for the determination of their crosslinking degree are thus very important. In this work, two semi‐empirical calorimetric methods are considered and compared to a scientifically sound rheological method used as a reference. The main purpose of this work is to reveal the chemical and physical fundamentals on which the two calorimetric methods are based, to allow for a scientific understanding of their advantages, and limitations. For one of these calorimetric methods, the so‐called “Melt‐Freeze” method, we have sought for a deeper understanding of the underlying crystallization physics through the use of successive self‐nucleation and annealing experiments, which give access to the crystallite size distribution of EVA, and to the influence of crosslinking upon it. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 866–876

Lamination Scheme of Curing Degree at Multiple Levels of Temperature With Location-Scale Regression

“…where z 1−α/2 is the 100(1−α/2)th percentile of the standard normal distribution. At a specific lamination temperature s, the sample size allocation (n 11 , n 12 , • • • , n 32 , n 33 ) affects the variance of the estimate of the optimal lamination time given in (11). So, it would be of interest to obtain the optimal sample size allocation in such an experiment.…”

“…Suppose the pre-fixed specifications for the curing degree are LSL = 65 and USL = 80. When the lamination process is set at temperature s = 147 • C, the estimated optimal lamination time and the corresponding estimated asymptotic variance are obtained as 12.7908 and 0.0815, respectively, upon substitutingθ into (8) and (11). These readily yield a 95% normal-approximate confidence interval (CI) as 12.7908 ± 1.96 √ 0.0815 = [12.2312, 13.3505].…”

“…where ∆H 1 and ∆H 2 are the reaction enthalpy of the uncured EVA reference and cured sample, respectively, can be used as an indicator to determine the degree of crosslinking on EVA. Much literature exists on methods for determining the degree of crosslinking by DSC and its applications (e.g., Bruckman et al [2]; Jaunich et al [7]; Ogier et al [11]); but, previous work has not dealt with optimal lamination time at different temperatures for the curing degree on EVA in a natural way, and this provides the main motivation for the present article. Optimal designs have many diverse applications in experimental designs (Cheng [3]; Jones & Majumdar [8]), in accelerated life and degradation tests (Tsai et al [14]; Hu et al [6]), and in clinical trials (Cheung et al [4]; Atkinson & Biswas [1]; Zang & Lee [17]).…”